1. Field of the Invention
This invention relates generally to the contraction of soft tissue, and more particularly, to the compaction of soft collagen tissue with minimal dissociation of collagen tissue.
2. Description of the Related Art
Instability of peripheral joints has long been recognized as a significant cause of disability and functional limitation in patients who are active in their daily activities, work or sports. Diarthrodial joints of musculoskeletal system have varying degrees of intrinsic stability based on joint geometry and ligament and soft tissue investment. Diathrodial joints are comprised of the articulation of the ends of bones and their covering of hyaline cartilage surrounded by a soft tissue joint capsule that maintains the constant contact of the cartilage surfaces. This joint capsule also maintains within the joint the synovial fluid that provides nutrition and lubrication of the joint surfaces. Ligaments are soft tissue condensations in or around the joint capsule that reinforce and hold the joint together while also controlling and restricting various movements of the joints. The ligaments, joint capsule, and connective tissue are largely comprised of collagen.
When a joint becomes unstable, its soft tissue or bony structures allow for excessive motion of the joint surfaces relative to each other and in directions not normally permitted by the ligaments or capsule. When one surface of a joint slides out of position relative to the other surface, but some contact remains, subluxation occurs. When one surface of the joint completely disengages and loses contact with the opposing surface, a dislocation occurs. Typically, the more motion a joint normally demonstrates, the more inherently loose the soft tissue investment is surrounding the joint. This makes some joints more prone to instability than others. The shoulder, (glenohumeral) joint, for example, has the greatest range of motion of all peripheral joints. It has long been recognized as having the highest subluxation and dislocation rate because of its inherent laxity relative to more constrained "ball and socket" joints such as the hip.
Instability of the shoulder can occur congenitally, developmentally, or traumatically and often becomes recurrent, necessitating surgical repair. In fact subluxations and dislocations are a common occurrence and cause for a large number of orthopedic procedures each year. Symptoms include pain, instability, weakness, and limitation of function. If the instability is severe and recurrent, functional incapacity and arthritis may result. Surgical attempts are directed toward tightening the soft tissue restraints that have become pathologically loose. These procedures are typically performed through open surgical approaches that often require hospitalization and prolonged rehabilitation programs.
More recently, endoscopic (arthroscopic) techniques for achieving these same goals have been explored with variable success. Endoscopic techniques have the advantage of being performed through smaller incisions and therefore are usually less painful, performed on an outpatient basis, are associated with less blood loss and lower risk of infection and have a more cosmetically acceptable scar. Recovery is often faster postoperatively than using open techniques. However, it is often more technically demanding to advance and tighten capsule or ligamentous tissue arthroscopically because of the difficult access to pathologically loose tissue and because it is very hard to determine how much tightening or advancement of the lax tissue is clinically necessary. In addition, fixation of advanced or tightened soft tissue is more difficult arthroscopically than through open surgical methods.
Collagen connective tissue is ubiquitous in the human body and demonstrates several unique characteristics not found in other tissues. It provides the cohesiveness of the musculoskeletal system, the structural integrity of the viscera as well as the elasticity of integument. These are basically five types of collagen molecules with Type I being most common in bone, tendon, skin and other connective tissues, and Type III is common in muscular and elastic tissues.
Intermolecular cross links provide collagen connective tissue with unique physical properties of high tensile strength and substantial elasticity. A previously recognized property of collagen is hydrothermal shrinkage of collagen fibers when elevated in temperature. This unique molecular response to temperature elevation is the result of rupture of the collagen stabilizing cross links and immediate contraction of the collagen fibers to about one-third of their original lineal distention. Additionally, the caliber of the individual fibers increases greatly, over four fold, without changing the structural integrity of the connection tissue.
There has been discussion in the existing literature regarding alteration of collagen connective tissue in different parts of the body. One known technique for effective use of this knowledge of the properties of collagen is through the use of infrared laser energy to effect tissue heating. The use of infrared laser energy as a corneal collagen shrinking tool of the eye has been described and relates to laser keratoplasty, as set forth in U.S. Pat. No. 4,976,709. The importance controlling the localization, timing and intensity of laser energy delivery is recognized as paramount in providing the desired soft tissue shrinkage effects without creating excessive damage to the surrounding non-target tissues.
Radiofrequency (RF) electrical current has been used to reshape the cornea. Such shaping has been reported by Doss in U.S. Pat. Nos. 4,326,529; and 4,381,007. However, Doss was not concerned with dissociating collagen tissue in his reshaping of the cornea.
Shrinkage of collagen tissue is important in many applications. One such application is the shoulder capsule. The capsule of the shoulder consists of a synovial lining and three well defined layers of collagen. The fibers of the inner and outer layers extend in a coronal access from the glenoid to the humerus. The middle layer of the collagen extends in a sagittal direction, crossing the fibers of the other two layers. The relative thickness and degree of intermingling of collagen fibers of the three layers vary with different portions of the capsule. The ligamentous components of the capsule are represented by abrupt thickenings of the inner layer with a significant increase in well organized coarse collagen bundles in the coronal plane.
The capsule functions as a hammock-like sling to support the humeral head. In pathologic states of recurrent traumatic or developmental instability this capsule or pouch becomes attenuated and the capsule capacity increases secondary to capsule redundance. In cases of congenital or developmental multi-directional laxity, an altered ratio of type I to type III collagen fibers may be noted. In these shoulder capsules a higher ratio of more elastic type III collagen has been described.
There is a need for a method and apparatus to effect controlled lineal contraction or shrinkage of collagen fibers to provide a multitude of non-destructive and beneficial structural changes and corrections within the body. More particularly with regard to the shoulder capsule, current surgical techniques involve cutting or advancing the shoulder capsule to eliminate capsular redundance or to otherwise tighten the ligamous complex. Accordingly, there is a need to control shrinkage of the capsule by utilizing the knowledge of the properties of collagen in response to a specific level of thermal application.